With the advance of technologies, the optical disk drive has become a well-accepted product to the general public. And with the information industry flourishing tremendously in recent years, the optical disk drive has become an indispensable product. For instance CD-ROM, DVD-ROM, and the like are very popular these days, and the technology is well developed.
At present, many optical disk drives have three light beams to perform server track control for the pickup head. A main light beam is used to read the data on the optical disk, and two secondary light beams are on two sides to correct the position of the main light beam. As the spindle motor and pickup head of the optical disk drive consist of many components, when these components are assembled, fabrication allowances of the individual components and the tolerance of the final assembly often result in a deviation between the spindle of the pickup head and the center of the optical disk. This deviation affects the positions of the two secondary light beams projecting on the optical disk. As the optical media density increases constantly, the interval of data tracks becomes narrower, and accurate control of the deviation becomes very important.
Refer to FIGS. 1 and 2 for conditions that have no deviation and a deviation between the spindle motor and pickup head of the optical disk drive, for a main light beam 10 and two secondary light beams 20 projecting on an optical disk track 30.
FIG. 1 illustrates the condition in which there is no deviation between the center of the optical disk and the pickup head. The main light beam 10 accurately projects in the center of the track 30 without any deviation.
FIG. 2 illustrates a condition in which the spindle motor deviates leftwards or rightwards. The relative positions of the track 30 and the three light beam spots on the optical disk are affected. The main light beam 10 moves away from the track 30, while the secondary light beams 20 move close to the track 30. As a result, the accuracy of the main light beam 10 of the pickup head to read data is affected, and the stability of the server track of the optical disk drive is reduced.